1. Field of the Invention
This invention relates to superconducting microwave components. More specifically, this invention relates to high frequency parts for treating electromagnetic waves having short wavelengths, such as microwaves, millimeter waves or others, and especially to constitutions of novel microwave components having conductor lines formed of oxide superconducting materials.
2. Related Background Art
Although the electromagnetic waves having wavelengths from tens of centimeters to some millimeters are called microwaves, millimeter waves or others are theoretically only a part of the electromagnetic wave spectrum, these electromagnetic waves are, in many cases, specially studied independently in the engineering field because special means and parts have been developed for treating these electromagnetic waves. The microwave line for guiding the electromagnetic waves in this band comprises a pair of conductor lines arranged through a dielectric and having one of the conductor lines grounded.
On the other hand, in 1988 (La,Ba).sub.2 CuO.sub.2 which exhibits superconductivity at 30K was discovered by Bednorz, Mueller, et al. In the next year 1987 YBa.sub.2 Cu.sub.3 O.sub.y having a critical superconducting temperature in the order of 90K was discovered by Chu, et al. In 1988 Maeda, et al. discovered the so-called Bi-based composite oxide superconducting material which exhibits a critical superconducting temperature exceeding 100K. Since these composite oxide superconductors can realize superconductivity by their being cooled by inexpensive liquid nitrogen, the possibility of practical applications of the superconducting technique has been suddenly noted.
The microwave components also enjoy the characteristic phenomena of superconductivity. That is, generally in a strip line the attenuation constant of a conductor due to a resistance is proportional to a square root of a frequency. The dielectric loss also increases with an increase of frequency. The dielectric loss in the recent strip lines is almost attributed mainly to a resistance of a conductor layer especially in the band equal to or lower than 10 GHz, due to the improvement of dielectric materials. Accordingly it improves the efficiency of the strip line to decrease the resistance of a conductor layer of the strip line. Strip lines not only can be used as mere transmission lines, but also can be patterned suitably to be microwave components, such as inductance devices, filters, resonators, delay lines, directional couplers, hybrids, etc. Accordingly the improvement of strip lines leads to the improvement of the characteristics of such microwave components.
FIG. 1 is a sectional view of a typical structure of a microwave component using oxide superconducting film as the conductor material.
As shown in FIG. 1, the microwave component comprises a first substrate 2 with a superconducting conductor line 1 formed thereon by patterning a superconducting film, a second substrate 4 with a superconducting grounding conductor 3 of a superconducting film formed thereon, which are laid on each other in a casing 5a. The casing 5a is sealed with a cover 5b, and a package is fabricated. Although not shown, a lead wire or the like is provided through the casing 5a or the cover 5b for introducing microwaves into the superconducting line 1.
This microwave component comprises two substrates for the following reason.
That is, generally a microwave component essentially includes a conductor line and a grounding conductor formed with a dielectric therebetween. On the other hand, in a superconducting microwave component, the conductor line and the grounding conductor are synthesized especially in thin films having good characteristics. But the technique of forming on the front side and the backside of one substrate film having the uniform characteristics requires a film forming operation of a high level. So far, the film forming level has not yet been practical. Presently the conductor line, and the grounding conductor are formed independently on separate substrates, and subsequently these substrates are laid on each other. And a microwave component using oxide superconducting films is prepared.
But it has been found that although a microwave component of the structure of FIG. 1 is actually fabricated, it does not exhibit required characteristics or has an extremely large loss.